1. Field of the Invention
The invention relates to piezoelectric ceramic materials which are effectively utilizable in various types of actuators and which are composed of ternary solid solutions having a fundamental composition of Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 -PbTiO.sub.3 -PbZrO.sub.3.
2. Description of the Prior Art
Piezoelectric ceramic materials used in actuators should have various characteristics such as a high piezoelectric constant, a high Curie point and high mechanical strength. One of piezoelectric materials which have been most widely used at present is a piezoelectric ceramic material composed of a ternary solid solution of Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 -PbTiO.sub.3 -PbZrO.sub.3. Many studies have been made on the above ceramic material in order to further improve the characteristics mentioned above. For instance, in order to improve the mechanical strength, there were proposed ceramic materials in Japanese Examined Patent Publication No. Sho 46-43062 in which a small amount of ZrSiO.sub.4 was added to the ternary solid solution of Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 -PbTiO.sub.3 -PbZrO.sub.3.
The improvement in strength of piezoelectric ceramic materials is needed especially when thin plates of piezoelectric ceramic materials are used in ultrasonic transducer elements or circuit elements. However, when this plates of piezoelectric materials are laminated for use as actuators, it is desirable to increase a degree of displacement of piezoelectric ceramic materials upon application of an electric field by increasing the piezoelectric constant of the materials rather than to improve the mechanical strength thereof.